Hot end won’t heat up

Hi I have a Lulzbot Taz workhorse and it keeps breaking. Now my current problem is the heater on the nozzle. I started a print with PETG at 275 degrees Celsius that print went well. Then I started another print with PETG and that also went well. After the last print I heat up the nozzle because I want to take out my filament and store it in a dry place. Like 15 seconds after I wanted the nozzle to heat, it sounds a warning. “Heater fault please reset printer”. I tried it again after reseting the printer. I look at the thermostat and it does not go up in temperature. Also don’t say my thermostat is broken because I replaced it with a new one recently.

My theories to the issue is.

Printer can’t handle 275.

Bad fuse.

Slicing software needs updated. Along with printer firmware.

Printer definitely can handle 275. If you’re not getting temps reported, it likely a bad thermistor, broken wiring.

Don’t say having replaced something recently means it’s not the source of the problem. Bad parts exist, and bad installations also happen. It could also be that whatever killed your previous thermistor killed this one.

That is a good point but. The thermistor is reading room temperature at 21 degrees Celsius. Also before I installed the thermistor I checked it with a multimeter and compared the results to the old thermistor
Here were the results.

(Old thermistor reading was 138.0 ohms. At room temperature it read 0 degrees Celsius.)

(New thermistor was 105.0 ohms and it reads correctly.)

Also, I just noticed PETG at 275 - that’s far above normal PETG printing temperature, even for using with a hardened extruder, is there a reason for running that high?

Back to the issue though, what toolhead are you using, and where did you source your thermistor?

Anytime the machine is reading a thermistor as 0 degrees, that typically means there’s no connection, not that it’s readings are off. Check what the multimeter is getting from the thermistor when measured from the controller side of the harness plug as you wiggle the wiring harness around, making sure it’s not losing connection. Do it as the hot end heats up, as thermal expansion may be separating a loose solder/crimp joint.

There is a reason for the high temperature. I am using a 0.5mm Hardened Steel nozzle and when I print my other materials I always go 10 or 15 degrees Celsius above the recommended temperature because of layer adhesion. I had some layer adhesion problems at 260 265 and 270 so 275 seems to give PETG a good amount of adhesion.

Printer and filament info

Filament brand: MatterHackers PRO PETG White

Bed temp 70 degrees Celsius

Hot end temp 275 degrees Celsius

Speed 45mm/s

Initial layer speed 15mm/s

Fan speed initial layer 0%

Fan speed regular 20%

Max fan speed 40%

Also I like the idea of the heat causing problems with the wires because I turned on my printer this afternoon to see if it would heat up, it did. So why did it heat up?

I will give the other wires a test on the multimeter.